Many agricultural combines use a rotary threshing or separating system. The system typically includes at least one rotor drivingly rotated within a perforated concave spaced radially outwardly thereof. The rotor will often have a frusto-conical inlet end having a helical flight or flights therearound for conveying a flow of crop material into a space between the rotor and the concave. The main body of the rotor will typically have one or more cylindrical or frusto-conical outer surface portions including threshing elements which protrude radially outwardly therefrom into the space and which are arranged in a pattern or array for conveying a mat of the crop material along a helical path through the space, while cooperating with features of the concave, e.g. bars or ribs, to separate larger components of the crop, namely crop residue commonly referred to as straw, which includes stalks, stems, cobs and the like, from the smaller grain and material other than grain (MOG). The straw is then typically propelled or carried rearwardly away from the threshing system for disposal, while the grain and MOG pass through the perforations of the concave to a cleaning system of the combine, typically located beneath the threshing system. Reference in this regard, Dunn et al. U.S. Pat. No. 4,248,249, and Tophinke U.S. Pat. No. 4,733,672, which illustrate representative prior art threshing system rotor and concave arrangements.
An important parameter for a successful threshing performance is the gap between the radial outer portions of the threshing elements, and the radial innermost features or portions of the surrounding concave. The setting of this gap is an operator function, and will typically be finely adjusted within a range of just a fraction of an inch or a few millimeters before or during operation to achieve a desired threshing capability or performance. Generally, if the gap is set too large, not enough grain will be separated from the straw, resulting in more grain loss. If the gap is too small, threshing quality may suffer, and in particular, the grain may be subjected to damage, particularly cracking, which is highly undesired in most instances. If there are irregularities in the outer cylindrical surface of the rotor on which the threshing elements are mounted, as the rotor is rotated past a particular region of the concave, the gap will vary. Also, if there is an eccentricity of the cylindrical surface, the gap will vary. And, if the rotor is not centered about the rotational axis thereof, during rotation the gap will vary. These conditions can also cause imbalance in the rotor, which can result in vibrations during rotation that can damage the rotor and other components of the threshing system, as well as other components of the combine, particularly at higher operating speeds. Vibration can also result in operator annoyance and discomfort.
The rotor is typically supported for rotation about a rotational axis extending through the center thereof, by a bearing on the inlet end, and a drive mechanism on the opposite end. The main body of the rotor is typically of riveted or welded sheet metal, and may include an internal support skeleton, for instance, comprising stiffening ribs or bulkheads, and a rear bulkhead which is connected to the drive mechanism. A problem that can be encountered with this construction is that, when the rotor is manufactured, it may have eccentricities, for instance, as a result of warpage from welding, uneven stress distribution, material variances, poor alignment during assembly, and the like. As another problem, in some common constructions the rear bulkhead is connected to the rear of the main body with fasteners around the circumference thereof, which has been found to allow water to enter the hollow interior of the rotor, which can cause imbalance during rotation, and corrosion.
Accordingly, what is sought is a rotor which, in operation, avoids one or more of the problems set forth above, particularly irregularities and eccentricity in the outer surface of the rotor and water collection, and an improved method for making the same which is simple and economical.